The role of the cyclic nucleotides in the effects of drugs on smooth muscle motility is a point of considerable controversy at present. It has been suggested that an increase in the intracellular concentration of cyclic AMP in a smooth muscle cell will result in relaxation of the muscle, whereas a decrease in cyclic AMP and/or an increase in cyclic GMP levels will cause the muscle to contract. A major objective of the proposed research will be to determine whether the changes in cyclic nucleotide levels reportedly caused by various smooth muscle stimulants and relaxants, are causally related to their effects on mechanical activity of the muscles. Isolated strips of uterine, intestinal and vascular smooth muscle will be clamp-frozen at various times after the addition of stimulant or relaxant drugs to the muscle baths. Cyclic nucleotide levels in the frozen tissues will be determined using standard techniques after preliminary purification of the tissue extracts by column chromatography. Attempts will be made to correlate changes in cyclic nucleotide levels with drug-induced contractions or relaxation, both on a temporal basis and on the basis of drug concentration. Smooth muscle relaxant drugs to be studied will include catecholamines, papaverine, nitroglycerin, tetracaine and diazoxide. Smooth muscle stimulants to be studied will include cholinergic drugs, prostaglandins, oxytocin and potassium-depolarizing solutions. The role of calcium in these responses, particularly with respect to the effects of stimulant drugs on cyclic GMP levels, will also be studied. In addition, the possible role of ovarian hormones in the response of the cyclic nucleotide systems in uterine muscle to various drugs, will also be investigated. These experiments may enable us to decide whether or not the cyclic nucleotides play a role in the regulation of smooth muscle tone and motility as has been recently suggested. BIBLIOGRAPHIC REFERENCE: Diamond, J. and Holmes T.G.: Effects of potassium chloride and smooth muscle relaxants on tension and cyclic nucleotide levels in rat myometrium. Canad. J. Physiol. Pharmacol. (In Press).